Fossil otoliths reveal changing predator-prey dynamics and partial resilience in reef fishes

Abstract

Predatory fishes are expected to regulate the abundances and body sizes of prey fishes on coral reefs, which may, in turn, have cascading effects across the food web. However, such top-down processes have been challenging to test, especially on Caribbean reefs where predator communities have been altered by centuries of selective harvesting, and therefore potentially function differently. To address this shifting baseline problem, we used Holocene fossil, archeological and modern fish remains (5758 otoliths and 807 shark denticles) to track changes in the relative abundances and body sizes of fishes of different functional and trophic modes on Caribbean reefs in Panama and the Dominican Republic over millennia. Piscivorous fish declined in relative abundance by 50-70% and became smaller since major human exploitation, which would have resulted in a decline in predation intensity since prehistoric times. In contrast, prey fishes like anchovy and damselfish became more abundant and larger over the same time period, consistent with a release from predation. Cryptobenthic fishes showed no change in body size or abundance over time, most likely because they are protected from predation and are controlled to a greater extent by habitat and food availability than predation. Our data support the hypothesis that predator loss has precipitated a release from predation for certain prey fish species, and yet despite this, some important facets of reef function have remained resilient over time.